Google Android chief Andy Rubin said through his Twitter account this morning that more than 500,000 Android devices are activated each day worldwide. Week over week, that's growth at a rate of 4.4 percent, he said.

My CNET colleague Don Reisinger notes that it was only a month ago that Google announced a 400,000-devices-per-day figure, up from 300,000 per day in December.

It's astounding growth, but the question is whether Google can control the beast. Android handsets are widely available, inexpensive to implement and offer the basic smartphone experience as we've come to know it in recent years: touchscreen, fast processor, multimedia and so forth.

It's the special sauce that fueled Android's staggering growth in the U.S. and is what continues to do so abroad, where smartphone adoption figures are beginning to mirror those seen in the early days in North America and Europe.

But there remain concerns about Google's ability to keep its various ducks in a row as rivals such as Microsoft and HP begin to execute on their mobile plans.

Still, in Q1 2011, Google and Apple were the only two companies to show growth in the industry-leading U.S. market, with 36.4 percent and 26.0 percent, respectively. (Microsoft held just 6.7 percent of its home market; HP just 2.6 percent.) Which goes to show that being a first-mover -- regardless of whether the product is ready to go to market -- matters.

Can the other companies stem Google's tide? I think so, if they focus on winning specific parts of the market where Google is stretched too thin. And we have yet to see how Nokia's eventual adoption of Microsoft Windows Phone 7 will play out in the global market.

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